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Abstract

The visible light photon counter (VLPC) is a very high quantum efficiency (QE, 88% at 694 nm) single photon detector in the visible wavelengths. The QE in the ultraviolet (UV) wavelenghths is poor in these devices due to absorption in the degenerate front contact. We introduce the ultraviolet photon counter (UVPC), where the QE in the near UV wavelength range (300-400 nm) is dramatically enhanced. The degenerate Si front contact of the VLPC is replaced with a Ti Schottky contact, which reduces the absorption of incident photons within the contact layer. We demonstrate a system QE of 5.3% at 300 nm and 11% at 370 nm for a UVPC with a Ti Schottky contact and a single layer MgF2 antireflection coating.

Figures (4)

(a) Schematic device structure of the VLPC. The VLPC consists of a number of Si epitaxial layers grown on a degenerate Si substrate. (b) Schematic device structure of the UVPC. The degenerately doped front contact of the VLPC is thinned and replaced with a Ti Schottky metal contact and a MgF2 AR coating. (Note: thicknesses not drawn to scale.)

The measured system QE of the VLPC and Si absorption coefficient at 10 K in the wavelength range of 300 – 650 nm is shown [11]. The QE drops sharply below 400 nm, which corresponds to a rapid increase in the absorption coefficient of Si. For wavelengths ≤ 370 nm, the input light level was increased to improve the SNR.

Current density-voltage (J-V) relationship of a 1000 μm diameter Ti Schottky diode with a MgF2 coating. Thermionic emission-diffusion theory was used to determine the p type barrier height. For clarity, data for all temperatures measured and used in the analysis are not shown.

The system QE and estimated lower bound for the internal QE of the UVPC and VLPC from 300 - 400 nm. The internal QE is estimated by accounting for losses in the fiber, output coupling efficiency, and detector coatings.